Rajeev Kumar - Academia.edu (original) (raw)
Papers by Rajeev Kumar
Journal of Magnetic Resonance, 2003
The selection of proper coherence pathways is a very important aspect of the design of NMR pulse ... more The selection of proper coherence pathways is a very important aspect of the design of NMR pulse sequences. This article describes a C++ program for the calculation of coherence pathway selection via phase cycles, including a module to calculate cogwheel cycles. Cogwheel phase cycles shorter than the original ones [M.H. Levitt et al., J. Magn. Reson. 155 (2002) 300] are derived and experimentally tested for the MQMAS experiment for 3/2 spins. Some other cogwheel cycles are derived for the MQNQMAS, the STMAS experiment, and a PFG diffusion pulse sequence. This program is publicly available through our website http://www.nyu.edu/projects/jerschow with additional documentation and examples.
Journal of Magnetic Resonance, 2005
We describe an NMR experiment that produces spectra correlating the first-order quadrupolar spect... more We describe an NMR experiment that produces spectra correlating the first-order quadrupolar spectrum and the central transition spectrum of half-integer quadrupolar spins, allowing one to separate the quadrupolar parameters in overlapping spectra under both static and magic-angle-spinning conditions. Promising fields of applications include situations where the sample cannot easily be rotated, or where it cannot be rotated at the magic angle.
Journal of Applied Polymer Science, 2003
Homopolymerization and copolymerization of N-(o-/m-/p-chlorophenyl) itaconimide with methyl metha... more Homopolymerization and copolymerization of N-(o-/m-/p-chlorophenyl) itaconimide with methyl methacrylate was carried out by taking varying mole fractions (0.1 to 0.5) of N-aryl substituted itaconimide monomers in the initial feed using azobisisobutyronitrile as an initiator and tetrahydrofuran as the solvent. The copolymer composition was determined by 1 H-NMR spectroscopy using the ratio of proton resonance signal intensity attributed to-OCH 3 of MMA (␦ ϭ 3.5-3.8 ppm) and the aromatic protons (␦ ϭ 7.0-7.5 ppm) of N-(o-/m-/p-chlorophenyl) itaconimide. The comonomer reactivity ratios were determined using Kelen-Tü dos and nonlinear error in variable methods. The reactivity ratios obtained by nonlinear error in variable methods were r 1 (PI) ϭ 1.26/r 2 (MMA) ϭ 0.35; r 1 (MI) ϭ 1.21/r 2 (MMA) ϭ 0.34; and r 1 (OI) ϭ 0.78/r 2 (MMA) ϭ 0.34. The carbonyl carbon signals of MMA (M) as well as N-aryl itaconimide (I) copolymers were used for the determination of the sequence distribution of M-and I-centered triads. The sequence distribution of M-and I-centered triads determined from 13 C{ 1 H}-NMR spectra of the copolymers are in good agreement with the triad concentrations calculated using the Alfrey-Mayo statistical model and Monte Carlo simulation method.
Journal of Molecular Structure, 2002
The copolymer composition of N-vinyl-2-pyrrolidone/butyl acrylate (V/B) copolymers was determined... more The copolymer composition of N-vinyl-2-pyrrolidone/butyl acrylate (V/B) copolymers was determined from the quantitative 13 C{ 1 H} NMR spectra. The monomer reactivity ratios for N-vinyl-2-pyrrolidone (V) and butyl acrylate (B) were found to be r V = 0 : 11 ± 0 : 07 ; r B = 0 : 54 ± 0 : 19 ; using the Kelen-Tudos and non-linear least-square error-invariable (EVM) methods. The 13C{ 1 H} and 1 H NMR spectra of these copolymers are overlapping and complex. The complete spectral assignment of the carbon and proton NMR spectra were done by employing distortionless enhancement by polarization transfer (DEPT) and twodimensional (2D) 13 C-1 H heteronuclear single quantum correlation spectroscopy experiments. The 2D total correlation spectroscopy (TOCSY) (1 H-1 H homonuclear TOCSY) NMR spectrum was used to ascertain the various geminal and vicinal couplings in the copolymer.
Journal of Magnetic Resonance, 2012
Environmental Chemistry, 2015
Environmental context Novel technology is used to examine oil contaminated soil to better underst... more Environmental context Novel technology is used to examine oil contaminated soil to better understand this longstanding problem. The data indicate that oil forms a non-discriminant layer over all the soil components, which in their natural state would be exposed to water, and that it retains certain polar compounds while contributing other oil contaminants to the surrounding porewater and groundwater. Such molecular level information helps to better understand the reoccurrence of hydrophobicity in remediated soil, and could lead to novel clean-up methods. Comprehensive multiphase (CMP) NMR spectroscopy is a novel NMR technology introduced in 2012. CMP NMR spectroscopy permits the analysis of solid, gel and liquid phases in unaltered natural samples. Here the technology is applied to control and oil contaminated soils to understand the molecular processes that give rise to non-wettable soils. 13C solid-state NMR spectroscopy is found to be excellent for studying the bulk rigid compone...
The chemical nature of xenobiotic binding sites in soils is of vital importance to environmental ... more The chemical nature of xenobiotic binding sites in soils is of vital importance to environmental biogeochemistry. Interactions between xenobiotics and the naturally occurring organic constituents of soils are strongly correlated to environmental persistence, bioaccessibility, and ecotoxicity. Nevertheless, because of the complex structural and chemical heterogeneity of soils, studies of these interactions are most commonly performed indirectly, using correlative methods, fractionation, or chemical modification. Here we identify the organic components of an unmodified peat soil where some organofluorine xenobiotic compounds interact using direct molecular-level methods. Using (19)F→(1)H cross-polarization magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR) spectroscopy, the (19)F nuclei of organofluorine compounds are used to induce observable transverse magnetization in the (1)H nuclei of organic components of the soil with which they interact after sorption. The observed (19)F→(1)H CP-MAS spectra and dynamics are compared to those produced using model soil organic compounds, lignin and albumin. It is found that lignin-like components can account for the interactions observed in this soil for heptafluoronaphthol (HFNap) while protein structures can account for the interactions observed for perfluorooctanoic acid (PFOA). This study employs novel comprehensive multi-phase (CMP) NMR technology that permits the application of solution-, gel-, and solid-state NMR experiments on intact soil samples in their swollen state.
Journal of Magnetic Resonance, 2012
Heterogeneous samples, such as soils, sediments, plants, tissues, foods and organisms, often cont... more Heterogeneous samples, such as soils, sediments, plants, tissues, foods and organisms, often contain liquid-, gel- and solid-like phases and it is the synergism between these phases that determine their environmental and biological properties. Studying each phase separately can perturb the sample, removing important structural information such as chemical interactions at the gel-solid interface, kinetics across boundaries and conformation in the natural state. In order to overcome these limitations a Comprehensive Multiphase-Nuclear Magnetic Resonance (CMP-NMR) probe has been developed, and is introduced here, that permits all bonds in all phases to be studied and differentiated in whole unaltered natural samples. The CMP-NMR probe is built with high power circuitry, Magic Angle Spinning (MAS), is fitted with a lock channel, pulse field gradients, and is fully susceptibility matched. Consequently, this novel NMR probe has to cover all HR-MAS aspects without compromising power handling to permit the full range of solution-, gel- and solid-state experiments available today. Using this technology, both structures and interactions can be studied independently in each phase as well as transfer/interactions between phases within a heterogeneous sample. This paper outlines some basic experimental approaches using a model heterogeneous multiphase sample containing liquid-, gel- and solid-like components in water, yielding separate (1)H and (13)C spectra for the different phases. In addition, (19)F performance is also addressed. To illustrate the capability of (19)F NMR soil samples, containing two different contaminants, are used, demonstrating a preliminary, but real-world application of this technology. This novel NMR approach possesses a great potential for the in situ study of natural samples in their native state.
Journal of Magnetic Resonance, 2003
The selection of proper coherence pathways is a very important aspect of the design of NMR pulse ... more The selection of proper coherence pathways is a very important aspect of the design of NMR pulse sequences. This article describes a C++ program for the calculation of coherence pathway selection via phase cycles, including a module to calculate cogwheel cycles. Cogwheel phase cycles shorter than the original ones [M.H. Levitt et al., J. Magn. Reson. 155 (2002) 300] are derived and experimentally tested for the MQMAS experiment for 3/2 spins. Some other cogwheel cycles are derived for the MQNQMAS, the STMAS experiment, and a PFG diffusion pulse sequence. This program is publicly available through our website http://www.nyu.edu/projects/jerschow with additional documentation and examples.
Journal of Magnetic Resonance, 2005
We describe an NMR experiment that produces spectra correlating the first-order quadrupolar spect... more We describe an NMR experiment that produces spectra correlating the first-order quadrupolar spectrum and the central transition spectrum of half-integer quadrupolar spins, allowing one to separate the quadrupolar parameters in overlapping spectra under both static and magic-angle-spinning conditions. Promising fields of applications include situations where the sample cannot easily be rotated, or where it cannot be rotated at the magic angle.
Journal of Applied Polymer Science, 2003
Homopolymerization and copolymerization of N-(o-/m-/p-chlorophenyl) itaconimide with methyl metha... more Homopolymerization and copolymerization of N-(o-/m-/p-chlorophenyl) itaconimide with methyl methacrylate was carried out by taking varying mole fractions (0.1 to 0.5) of N-aryl substituted itaconimide monomers in the initial feed using azobisisobutyronitrile as an initiator and tetrahydrofuran as the solvent. The copolymer composition was determined by 1 H-NMR spectroscopy using the ratio of proton resonance signal intensity attributed to-OCH 3 of MMA (␦ ϭ 3.5-3.8 ppm) and the aromatic protons (␦ ϭ 7.0-7.5 ppm) of N-(o-/m-/p-chlorophenyl) itaconimide. The comonomer reactivity ratios were determined using Kelen-Tü dos and nonlinear error in variable methods. The reactivity ratios obtained by nonlinear error in variable methods were r 1 (PI) ϭ 1.26/r 2 (MMA) ϭ 0.35; r 1 (MI) ϭ 1.21/r 2 (MMA) ϭ 0.34; and r 1 (OI) ϭ 0.78/r 2 (MMA) ϭ 0.34. The carbonyl carbon signals of MMA (M) as well as N-aryl itaconimide (I) copolymers were used for the determination of the sequence distribution of M-and I-centered triads. The sequence distribution of M-and I-centered triads determined from 13 C{ 1 H}-NMR spectra of the copolymers are in good agreement with the triad concentrations calculated using the Alfrey-Mayo statistical model and Monte Carlo simulation method.
Journal of Molecular Structure, 2002
The copolymer composition of N-vinyl-2-pyrrolidone/butyl acrylate (V/B) copolymers was determined... more The copolymer composition of N-vinyl-2-pyrrolidone/butyl acrylate (V/B) copolymers was determined from the quantitative 13 C{ 1 H} NMR spectra. The monomer reactivity ratios for N-vinyl-2-pyrrolidone (V) and butyl acrylate (B) were found to be r V = 0 : 11 ± 0 : 07 ; r B = 0 : 54 ± 0 : 19 ; using the Kelen-Tudos and non-linear least-square error-invariable (EVM) methods. The 13C{ 1 H} and 1 H NMR spectra of these copolymers are overlapping and complex. The complete spectral assignment of the carbon and proton NMR spectra were done by employing distortionless enhancement by polarization transfer (DEPT) and twodimensional (2D) 13 C-1 H heteronuclear single quantum correlation spectroscopy experiments. The 2D total correlation spectroscopy (TOCSY) (1 H-1 H homonuclear TOCSY) NMR spectrum was used to ascertain the various geminal and vicinal couplings in the copolymer.
Journal of Magnetic Resonance, 2012
Environmental Chemistry, 2015
Environmental context Novel technology is used to examine oil contaminated soil to better underst... more Environmental context Novel technology is used to examine oil contaminated soil to better understand this longstanding problem. The data indicate that oil forms a non-discriminant layer over all the soil components, which in their natural state would be exposed to water, and that it retains certain polar compounds while contributing other oil contaminants to the surrounding porewater and groundwater. Such molecular level information helps to better understand the reoccurrence of hydrophobicity in remediated soil, and could lead to novel clean-up methods. Comprehensive multiphase (CMP) NMR spectroscopy is a novel NMR technology introduced in 2012. CMP NMR spectroscopy permits the analysis of solid, gel and liquid phases in unaltered natural samples. Here the technology is applied to control and oil contaminated soils to understand the molecular processes that give rise to non-wettable soils. 13C solid-state NMR spectroscopy is found to be excellent for studying the bulk rigid compone...
The chemical nature of xenobiotic binding sites in soils is of vital importance to environmental ... more The chemical nature of xenobiotic binding sites in soils is of vital importance to environmental biogeochemistry. Interactions between xenobiotics and the naturally occurring organic constituents of soils are strongly correlated to environmental persistence, bioaccessibility, and ecotoxicity. Nevertheless, because of the complex structural and chemical heterogeneity of soils, studies of these interactions are most commonly performed indirectly, using correlative methods, fractionation, or chemical modification. Here we identify the organic components of an unmodified peat soil where some organofluorine xenobiotic compounds interact using direct molecular-level methods. Using (19)F→(1)H cross-polarization magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR) spectroscopy, the (19)F nuclei of organofluorine compounds are used to induce observable transverse magnetization in the (1)H nuclei of organic components of the soil with which they interact after sorption. The observed (19)F→(1)H CP-MAS spectra and dynamics are compared to those produced using model soil organic compounds, lignin and albumin. It is found that lignin-like components can account for the interactions observed in this soil for heptafluoronaphthol (HFNap) while protein structures can account for the interactions observed for perfluorooctanoic acid (PFOA). This study employs novel comprehensive multi-phase (CMP) NMR technology that permits the application of solution-, gel-, and solid-state NMR experiments on intact soil samples in their swollen state.
Journal of Magnetic Resonance, 2012
Heterogeneous samples, such as soils, sediments, plants, tissues, foods and organisms, often cont... more Heterogeneous samples, such as soils, sediments, plants, tissues, foods and organisms, often contain liquid-, gel- and solid-like phases and it is the synergism between these phases that determine their environmental and biological properties. Studying each phase separately can perturb the sample, removing important structural information such as chemical interactions at the gel-solid interface, kinetics across boundaries and conformation in the natural state. In order to overcome these limitations a Comprehensive Multiphase-Nuclear Magnetic Resonance (CMP-NMR) probe has been developed, and is introduced here, that permits all bonds in all phases to be studied and differentiated in whole unaltered natural samples. The CMP-NMR probe is built with high power circuitry, Magic Angle Spinning (MAS), is fitted with a lock channel, pulse field gradients, and is fully susceptibility matched. Consequently, this novel NMR probe has to cover all HR-MAS aspects without compromising power handling to permit the full range of solution-, gel- and solid-state experiments available today. Using this technology, both structures and interactions can be studied independently in each phase as well as transfer/interactions between phases within a heterogeneous sample. This paper outlines some basic experimental approaches using a model heterogeneous multiphase sample containing liquid-, gel- and solid-like components in water, yielding separate (1)H and (13)C spectra for the different phases. In addition, (19)F performance is also addressed. To illustrate the capability of (19)F NMR soil samples, containing two different contaminants, are used, demonstrating a preliminary, but real-world application of this technology. This novel NMR approach possesses a great potential for the in situ study of natural samples in their native state.